1. Field of the Invention
The present invention relates to integrated or xe2x80x9cplanarxe2x80x9d optical waveguide devices, and particularly to xe2x80x9cathermalxe2x80x9d devices in which the light-transmitting properties are generally insensitive to temperature fluctuations.
2. Technical Background
Integrated or xe2x80x9cplanarxe2x80x9d optical waveguide devices, such as integrated optical circuits, combine miniaturized waveguides and optical devices into a functional optical system incorporated onto a small planar substrate. Such integrated optical waveguide devices are utilized in optical communications systems, usually by attaching optical waveguide fibers that transmit light signals to the integrated optical waveguide device as inputs and outputs. The integrated optical waveguide device performs one or more functions or processes on the transmitted light. Such devices provide good performance at consistent standard room temperatures, but exhibit poor performance when used in environments where they are exposed to thermal variations or fluctuations. The wavelength channels processed by the integrated optical waveguide device tend to shift with changes in operating temperatures. Integrated optical devices which incorporated optical path length differences can be used as wavelength multiplexing and demultiplexing devices. Such integrated optical devices are particularly useful as a wavelength division multiplexer/demultilexers, and may incorporate a phased array made from a plurality of different waveguide core arms which have differences in optical path length.
It has been found that the use of integrated optical waveguide devices is limited by their temperature dependence. In such integrated devices, thermal channel wavelength shifts of greater than 0.10 nm/xc2x0 C. at a transmitting wavelength in the 1550 nm range can limit their usefulness in environments of differing temperature. Presently, the application of such integrated optical waveguide devices has been hindered by the requirement to consistently maintain the temperature of the device such as by actively heating or cooling the device. While such costly and energy consuming heating and cooling may suffice in a laboratory setting, there is a need for an integrated optical waveguide device that is manufacturable and can be deployed in the field and operate properly when subjected to temperature changes.
The present invention is directed to an integrated optical waveguide device that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art. The present invention provides an athermalized polymer overclad integrated planar optical waveguide circuit device which inhibits the shifting of channel wavelengths due to variations in operating temperature within a predetermined operating temperature range. In a preferred embodiment the invention provides an athermalized phased array wavelength division multiplexer/demultiplexer.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus, compositions, and methods particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention provides an integrated optical waveguide circuit device that includes a doped silica waveguide circuit core supported on a planar substrate. The planar substrate is a solid flat substrate (such as a silica wafer or a silicon wafer) which may further include an underclad or buffer layer (such as an undoped or lightly doped silica layer). The doped silica waveguide circuit core has a first waveguide path and at least a second waveguide path, wherein the waveguide paths have a difference of xcex94L of path length that is selected to provide an optical path difference which corresponds to suitable channel wavelengths xcex in the range of 1500-1600 nm and to a suitable free spectral range (with respect to the number of channels and to the channel spacing). The device includes a polymer overclad which clads the doped silica waveguide circuit core. The polymer overclad covers and encapsulates the waveguide circuit core, wherein light guided by the circuit core, the polymer overclad, and the planar substrate propagates in the circuit core, the polymer overclad and the planar substrate with the polymer overclad having a negative variation in refractive index versus temperature (dn/dT). The polymer overclad is selected such that the polymer overclad""s negative variation in refractive index versus temperature (dn/dT) restricts the shift in the channel wavelength xcex to less than 0.1 nm when the device is subjected to a temperature variation within the operating range of 0xc2x0 to 70xc2x0 C. In a preferred embodiment the device is a wavelength division multiplexer/demultiplexer with the waveguide paths forming a phased array.
In another aspect, the invention includes an athermalized integrated optical phased array wavelength division multiplexer/demultiplexer having a doped silica waveguide core on a planar substrate that is overclad with a polymer overclad comprised of fluorinated monomers.
In a further aspect, the invention comprises a method of making an optical waveguide wavelength division multiplexer/demultiplexer device. The method includes the steps of providing a planar substrate, and forming a doped silica waveguide core on the planar substrate with the waveguide core incorporating an optical path length difference which corresponds to a channel wavelength xcex in the wavelength range of 1500-1600nm. The method further includes overcladding the doped silica waveguide core with a polymer overclad having a negative variation in refractive index versus temperature (dn/dT), wherein the polymer overclad inhibits the shift of the channel wavelength xcex when the device is subjected to a variation in temperature.